Apparatus for correcting bombsights



Dec. 26, 1961 R. D. WYCKOFF APPARATUS FOR CORRECTING BOMBSIGHTS 2SheetS-Shet 1 Filed June 19, 1946 ,I 1 ;c' 3'. Z

BOMB RELEASE COURSE OF BQMBING PLANE SIGHTING ANGLE Rn Do lv RALPH D.WYCKOEFF 2 Sheets-Sheet 2 -Ill R. D. WYCKOFF APPARATUS FOR CORRECTINGBOMBSIGHTS ,i 1 ';t'c5

ELEVATOR JNTEGRHTOR Dec. 26, 1961 Filed June 19, 1946 RUBBER INTEGRHTO'RRALPH D. WYCKOFF United States Patent 3,014,280 APPARATUS FOR CORRECTINGBOMBSIGHTS Ralph D. Wyckolf, Pittsburgh, Pa., assignor to Gulf Research& Development Company, Pittsburgh, Pa., a corporation of Delaware FiledJune 19, 1946, Ser. No. 677,879 12 Claims. (Cl. 3346.5)

This invention relates to improvements in bombsights, and in particularconcerns apparatus whereby the bombing accuracy elicited by such abombsight is greatly improved when the same is used in conjunction withand for the aiming of dirigible bombs of the high-angle type.

In the bombing of targets from airplanes it has been found possible togreatly increase the accuracy by employing a remotely controllable orsteerable bomb. Examples of such bombs are described in copendingapplications, one of which is entitled Dirigible Bomb by Wyckoif,Molnar, Palmer and Blewett, Ser. No. 673,374, filed May 31, 1946, nowPatent 2,466,528, and another entitled Dirigible Bomb by Wyckoif,Fitzwilliam and Salvetti, Ser. No. 673,372, filed May 31, 1946, nowPatent 2,495,304. Both of the above described dirigible bombs areremotely steered by radio signals. They are launched at a relativelyopportune moment by reference to a conventional bombsight which may forexample be of the well-known Norden type. It has been found that forcertain types of dirigible bombs it is advantageous to follow the courseof the bomb after launching by observation through the bombsight andmake the necessary steering corrections by reference to an index in thefield of view. This invention comprises the method and apparatusnecessary for correcting the bombsight for errors in timing which areintroduced as a result of the bombardiers eiforts to steer the bombafter release.

The type of high-angle dirigible bomb, described in the abovementionedWyckoif, Molnar, Palmer and Blewett application is controlled only inazimuth and is best steered by direct sighting after release from thebombing airplane. Thus, after the release the bombardier dispenses withthe sight and follows the bomb with unaided eye, a flare on the tail ofthe bomb providing adequate visibility throughout its fall to thetarget. Azimuth errors of the order of ten feet may thus bedistinguished even from altitudes of 20,000 ft.

An improved type of high-angle dirigible bomb, which is described in theabovementioned Wyckoif, Fitzwilliam and Salvetti application, may becontrolled in both azimuth and range and requires a special bombsight inorder to provide a criterion for range steering. It will be clear thatin direct observation of the bomb in flight from the vantage point ofthe bombardier in the bombing airplane, the bomb (flare) appears totravel horizontally along the ground, all impression of verticalperspective having disappeared in the first few thousand feet of fallbecause binocular vision loses its effectiveness at great distances.Thus the observer, stationed in the bombing airplane in continuedstraight-line flight directly over the falling bomb, is quite incapableof judging the height of the bomb above the target area and cannotpredict the time of impact. Such prediction of the time of impact isessential for an accurate hit.

The obvious remedy and indeed the only means of accomplishing rangesteering by direct sight without prediction of the moment of impact isto maneuver the bomb, the air-plane, or both so as to eclipse the targetby the bomb. If this be accomplished accurately, the bomb must hit thetarget regardless of just when impact occurs. Unfortunately this methodof range sighting requires far more maneuverability of the bomb than isattainable with the usual type of high-angle dirigible bomb. Moreover,

the combined bomb and bomber maneuver requires a maneuver of the bombingplane that is rather drastic for the usual heavy bomber and hence isconsidered impractical for such airplanes.

The alternative to direct sighting of a range controlled type of bomb isto effect range steering by the use of a special bombsight in which boththe bomb and the target are visible and the instant of impact ispredicted by a suitable sight mechanism. This invention comprises amethod and apparatus for accurately adjusting this prediction inaccordance with the direction and amount of steering applied to the bombduring the course of its fall.

From any given altitude the time of flight of a particular type ofstandard bomb is constant within 0.1-0.2 second, the principal cause ofvariation being uncertainty in the exact altitude above the target atwhich the release of the bomb occurs. This fact is used in all standardbombsights. 'For example, in the well-known Norden sight this predictedtime of fall is put into the bombsight mechanism by the bombardier assoon as his bombing altitude is determined. Similarly, with a rangecontrolled bomb, suitable ballistic tables may be prepared giving theaverage time of fall of the bomb for the particular altitude desired. Tothe extent that such tables provide prediction accurate to a firstapproximation of the time of fall of the bomb, this time put into thebombsight will provide the criterion for predicting its time of impact.The principle of operation of such a sight can be illustrated by thefollowing considerations and by reference to FIGURE 1 which shows aschematic diagram of a bombing run and the angles and bomb path to beconsidered. FIGURE 1 also shows diagrammatically the geometricalrelationship between bomber, bomb and target at the release of the bomb,at an intermediate instant during the steered fall of the bomb, and atthe moment of impact.

It is customary for the bomber airplane to be flying at a constant andaccurately known altitude above the target and in a straight line headeddirectly over the target as illustrated in FIG. 1. At the start of thebombing run the bombardier will sight the target at an angle to thevertical and as he approaches the target this sighting angle willgradually decrease to zero when he is directly over the target. Nowsuppose that at an appropriate time during this approach the bomb isreleased and the bomber continues on course with constant speed. Sinceat release the bomb has the same horizontal velocity as the bomber, andneglecting wind resistance, it will continue its forward motion withundiminished velocity. From the bombardiers viewpoint the bomb willappear to fall in a vertical line directly below him and if he wereprovided with a vertical telescope the bomb would remain in the field ofview of this telescope throughout its fall. In an actual case wind dragon the falling bomb cannot be neglected, and, instead of remaining in avertical line projected downward from the moving bomber, the bomb willactually trail behind the vertical at a substantially constant angleknown as the trail angle. However, for the purpose of this discussion wewill continue to ignore the trail angle and assume that the bomb followsa truly parabolic trajectory in space; hence, as seen from the bombertraveling at an equal forward velocity, the bomb will appear to remainvertically below the observer.

Now let us equip this same telescope with a split field of view obtainedby interposing a suitable moving mirror on its optical axis, such thatby adjusting the angle of this mirror the bombardier simultaneously canobtain a line of sight forward of the vertical into the target. At theinstant of release of the bomb these two lines of sight (the verticalcontaining the bomb and the one to the target) will have a certain anglecalled the dropping angle. If we now provide a motor mechanism to rotatethe moving mirror so as to cause this angle gradually to decrease tozero, the bomb and the target can be made to remain in viewsimultaneously throughout the drop provided the proper goemetricalconsiderations are introduced and the proper rate of closure of thetarget angle to the vertical, or bomb angle, is maintained. Moreover, ifthe total time of closure of the two lines of sight is made exactlyequal to the time of fall of the bomb, impact of the bomb will occur atthe instant the two lines of sight coincide. Now let us suppose that thebombardier steers the bomb in such a manner that, in his sight, the bombis always superposed on the target. This assures that the bomb iseclipsing the target at the instant his two lines of sight coincide, andsince the timing of this closure has been made to agree with thepredicted impact time, the bomb must hit the target.

With such a sight the only factor which could possibly cause an error inthe hit would be failure of the impact to occur at the predicted instantthat the two sighting angles coincide. With sufficient maneuverabilityavailable in the bomb and sufficient skill in manipulation of thesteering controls to permit the bombardier to maintain superposition ofthe bomb and target images in his sight, there are no limitationsimposed other than accurate timing. Thus the vertical line of sight neednot be actually vertical, the dropping angle need not be thatappropriate to an accurate hit, and the bombing plane need not maintaina perfectly constant speed or straight-line course. In fact, the onlyrequirement is that the bombardier be able to keep the bomb and targetin view in his sight and have sutficient maneuverability in the bomb tobring the two images into eclipsing position before impact occurs. Thiswill be evident on considering that in effect, the bombardier has twolines of sight, the target being at the end of one line, with the bombtraveling down along the other at such a rate that when the anglebetween the two lines is closed to zero, the bomb has traveled exactlythe vertical distance to the target. In the view through the sight,impact of the bomb will occur exactly when the angle closes to zero andit will be on the target, and to an observer on the ground the actualspace trajectory of the bomb will intersect the ground at the targetpoint.

This independence of steering on all factors except timing is, ofcourse, indicative of the practicability of removing sighting or bombingrelease errors of all kinds and also of producing a hit on a targetwhich has maneuvered out of position after release of the bomb. However,it is also evident that if the bomb has been sighted and releasedperfectly so that no steering is required, the bombardier would be awareof this fact only if the sight has been designed not only for propertiming of the closure of the bomb and target angle, but also with theproper type of motion in the moving mirror to track perfectly for anormal trajectory.

A modification of the well-known Norden bombsight may be made to fulfillthe above requirements. The mechanism of the Norden bombsight through asuitable rotating mirror in effect maintains the objective of thesighting telescope pointed toward the target. The modification requiredis the addition of an auxiliary bomb-tracking mirror which comprises afixed partial mirror at the entrance or objective end of the bombsighttelescope, this mirror being placed at such an angle so as to provide afixed vertical" field of view. As is well known, this vertical ismaintained substantially in the true vertical by the Norden sight gyrostabilizers.

For the sake of simplicity, I have here spoken of the line of sight tothe bomb being in the vertical. This would be true only in a vacuum inwhich the bomb trajectory would be truly parabolic. In practice, airresistance introduces an aerodynamic drag on the bomb which causes it totrail behind a true parabola by an angle which is almost constant andwhich is known as the trail angle. This detail, which may be allowed forin the adjustment of th bombsight, is not pertinent to the understandingof my invention and need not be considered further.

The above discussion is presented to permit a proper understanding ofthe type of bombsight used in steering high-angle dirigible bombs inorder that my improvement on this sight may be comprehended.

It has been mentioned that fundamentally all bombsighting techniques arebased on timing of the sight to match the predicted time of fall of thebomb. The fact has been stressed that the accuracy of the abovedescribed modified bombsight for use with dirigible bombs is verydefinitely predicated on the degree of precision with which thisequality in timing is attained. It should be clear, for example, that ifthe bombardier has steered the bomb so that it is eclipsing the targetwhen the lines of sight to the target and the bomb coincide, the bombmust have arrived at the ground at exactly that instant of coincidenceif a perfect hit in range is secured. If, however, the fall of the bombhas exceeded the predicted time, it will still be in the air over thetarget at the moment of coincidence and hence will overshoot the targetthough the bombardier would be unaware that this overshoot wasimpending. Similarly, if the time of fall is less than that predicted,the bomb must undershoot the target. Evidently the amount of this errorwill be the total error in timing At multiplied by the horizontalcomponent V or ground velocity of the bomb, namely (ALV In the case ofstandard bombs or, in fact, dirigible bombs which are allowed to falluncontrolled, the time of fall of any individual bomb from a givenaltitude will vary but little from the average time of fall of bombs ofidentical weight and structure. By using modern radioaltimeters thealtitude of the bomber over the target may be determined with an errorof the order of :50 ft, which may be ignored. Thus for normaluncontrolled bombs the actual time of fall will usually be within :0.1second of the value obtained from the ballistic tables for theparticular type of bombs involved.

This constancy of the time of fall for a given altitude is, of course,predicated upon a constant drag coefficient or air resistance. Now inthe case of dirigible bombs, the drag coefficient has a fixed value onlyin an uncontrolled drop, for steering the bomb involves aerodynamicallyderived lift forces which result in increase in wind resistance due toinduced drag. Thus the controlled bomb is subjected to the normal dragplus an induced drag due to steering, with the result that such a bombwill, in general, fall slower by an amount depending upon the amount ofsteering required. 'For example, in actual practice with considerableerrors to be corrected, the time of fall may be as much as 2.0 secondsgreater than for an uncontrolled bomb and, appearing as a tinting error,would result in overshooting the target 300 ft. or more on a typical15,000 ft. drop, even though the bombardiers steering appeared perfectin his sight. It is the purpose of the present bombsight improvement tominimize such errors by applying suitable compensating corrections tothe timing of the bombsight.

Since, in general, the effect of steering is always to increase the timeof fall it is possible to ameliorate the resulting error by usingballistic tables in which an increment of time has been added to thetime of fall for an uncontrolled bomb, the added increment being such asto compensate for an average amount of steering. However, bombing errorsencountered in practice, or the bombing of a maneuvering target, mayinvolve a wide diversity in the amount of steering required to afiect ahit. Hence it is impossible to derive an average time incrementapplicable to all cases. On the other hand, I have found that there is areasonably accurate relation between the amount of steering and theincrement added to the time of fall which permits reasonably accurateprediction of the time increment which may then be applied as acorrection to the timing of the bombsight.

When this correction is made by the method and apparatus of thisinvention a very high degree of bombing accuracy is obtained.

It will be further evident that if up-elevator is applied to a dirigiblebomb, the left brought into play has an upward component which opposesthe acceleration of gravity, thus slowing up the fall. This is an effectdistinct from the induced drag and is additive thereto. On the otherhand, down-elevator will produce a lift force having a downwardcomponent aiding gravity and hence speeding the fall. Therefore, in thecase of down-elevator the downward lift component and the induced dragare opposite in sign, thereby requiring a smaller net correction. Thus,in the case of elevator applications, in addition to the induced dragthere is an additional effect which is additive in the case ofup-elevator and subtractive for down-elevator. Thus the correctionrequired is one which varies also with the direction of steering appliedto the bomb.

Having discovered that a predictable relation exists between theduration of rudder and/or elevator applications and the increment oftime added to the normal time of fall, it is accordingly an object ofthis invention to provide means for adjusting the bombsight whereby thispredicted time increment may modify the bombsight timing to eliminatethe range error normally caused by steering effects which modify thenormal ballistic time.

It is a further object of this invention to provide means forintroducing into a bombsight a time increment correction in proportionto a predicted time increment caused by steering elfects which modifythe normal ballistic time.

It is a further object of this invention to provide means whereby thetiming of a bombsight may be continually adjusted while the bomb isfalling for time errors introduced by steering of a dirigible bomb.

It is a still further object of this invention to provide means wherebythe timing of a bombsight may be adjusted while the bomb is falling,such adjustment being made at a rate which varies with the direction ofsteering applied to the bomb.

It is a still further object of this invention to provide a bombsightfor use with a dirigible bomb, such that when used together with a bombcontrollable in both range and azimuth allows attainment of a bombingaccuracy many times greater than has heretofore been attainable.

In the dirigible type bombs described in the abovementioned copendingapplications, control is achieved by yawing or pitching the entire bombunder control of the rudder or elevator flaps, in order to produce thenecessary aerodynamic lift forces. The simplest form of controldescribed therein is an on-oif type of control, so that with controlapplied the bomb responds with its full and constant trim angle ofattack. Thus the induced drag accompanying a control is repeated in fullmagnitude with each application. This type of control is advantageousover proportional type of control for purposes of making the timingcorrections. Moreover, since the drag iricrements due to yaw or pitchare equal, and because the curve of induced drag vs. yaw angle is knownto follow a square law, the drag eifects of yaw and pitch will beadditive if both are applied simultaneously. Actually, because ofsomewhat complex considerations this simple relation does not applyexactly throughout the trajectory. However, in an average drop thesteering is usually applied during approximately the same part of theflight and as a result statistical data has shown that for a givendirigible bomb a numerical constant b may be derived such that whenmultiplied by the total duration of rudder application the incrementaltime of fall is obtained with reasonable accuracy. Similarly, this sameconstant would apply to elevator applications insofar as induced drag isconcerned, but there are other factors involved in the elevatorapplication.

Again statistical data provides a numerical constant a which multipliedby the total time of up-elevator application gives the total incrementof time added to the fall. Similarly the effect of down-elevator may beexpressed by a third coefiicient c which, depending on the relativemagnitude of the induced drag and the downward lift component, may beeither slightly positive or negative in value depending on theparticular type of bomb.

The derivation from statistical ballistic data of the coefficients a, b,and c and their significance have been shown. Thus:

ue ue At =CT At =bT (3) where:

At =total added time of flight due to up-elevator application.

At =total added time of flight due to down-elevator application.

At =total added time of flight due to rudder applications.

T T T =total duration of up, down, or rudder applications, respectively.

In principle, therefore, I have found that, to a close approximation theincremental time of fall affecting a dirigible bomb may be representedas a product of the integrated time of application of a particularcontrol and a numerical coefiicient.

In a simple embodiment of a correcting device a small motor may becaused to rotate at a speed a revs/sec. during the time an up-elevatorcontrol is applied. The total revolutions of this motor will then beproportional to At the total time added to the bombs flight due totip-elevator applications. Similarly the total revolutions of anothermotor of speed b revs/sec. operating in like fashion when rudder isapplied will provide a measure of the rudder effect. A third similardevice will handle the down-elevator effect. Since the controlapplications are transmitted from the bombing plane to the bomb by radioand the control signals originate in the bombing plane, it is a simplematter to couple the bombardiers control stick to the corrector deviceso that the separate corrector elements are actuated during the controloperation.

Having thus described in principle the method of deriving a measure ofthe correction time desired, the method by which this quantity may beapplied to the bombsight to effect the proper correction in sighting thebomb will now be described.

The properties of the bombsight used in dirigible bombing have beenoutlined and to those skilled in the art, the manner of accomplishingthese properties will be clear. The mechanism of the sight providesknown means for synchronizing the motion of the line of sight to thetarget so that the cross hair remains at least approximately on thetarget during the bombing run. Means are also provided whereby for anygiven altitude a certain timing, termed by those versed in the art asthe disc speed, may be set into the sight by the bombardier, this speedbeing a function of the type of bomb used and determined from suitableballistic tables. With these essential quantities put into the sight andother operational adjustments made, the bomb is then releasedautomatically by the sight at the proper moment. The angle between thevertical and the line of sight to the target is called the droppingangle. Now, while this dropping angle is variable and will depend uponvarious factors such as altitude, air speed, windage, etc., it is aproperty of the ordinary sight mechanism that the time from the instantof release to closure of the target line of sight into the auxiliaryline of sight to the bomb will be a constant and equal to the desiredtime set into the sight as the disc speed.

It will now be evident that the time corrector device which is thesubject of the present invention is intended to modify the normal timingof the sight by the incremental time as derived by the correctormechanism in accordance with the integrated steering operations. Forexample: In an uncontrolled drop the time of fall of a particulardirigible bomb from 15,000 ft. is 31.9 seconds and coincidence of thelines of sight to bomb and target will occur 31.9 seconds after releasein a properly adjusted bombsight. However, in order to correct a largeaiming error and cause the bomb to eclipse the target in the sight asrequired suppose the bombardier applied, say, 10 seconds of up-elevatorto the bomb. The resulting steering effect will add some 2.0 seconds tothe time of fall with the result that, as explained earlier, the bombwill be directly over the target 2 seconds before impact and will besome 340 ft. beyond the target at the moment of impact if the horizontalcomponent of velocity is, say, 170 ft./sec. On the other hand, had thebombsight coincidence been delayed the required 2 seconds by a suitablecorrecting device, coincidence and bomb impact would have beensimultaneous, and the hit would occur precisely in accordance with therelative positions of bomb and target as seen in the bombsight. Thus themethod of this invention is to modify the relative motion of thebombsight lines of sight by an amount equal to the incremental timeinduced by steering. This may be done by a simple displacement of therelative angular position of the auxiliary bomb-tracking mirrorpreviously described and the target-tracking mirror. The required motionmay be put into either mirror for purposes of this invention. However,it is preferable for reasons of expedient design to apply the correctionto the moving target-tracking mirror. This may be accomplished by anysuitable differential gear or similar device whereby both the normalmirror motion and the desired correcting motion may be introducedindependently. I do not limit myself to the details of the correctingmeans for carrying out the method of my invention here disclosed by wayof example. It is merely necessary that the proper incremental timecorrection be superimposed on the angular tracking rate or disc speed.

In order to illustrate how the objects of my invention may beaccomplished, and one means whereby my method of bombsight correctionmay be applied, reference is made to the following figures forming apart of this invention specification:

FIG. 1 already referred to, shows a schematic diagram of a bombing runand the dual lines of sight which are superimposed in the bombsight,showing also the geometrical relationship between the bomber, bomb andtarget at the release of the bomb, at an intermediate time representingan instant during the steering operation, and at the moment of impact;

FIG. 2 shows schematically one type of integrating mechanism which maybe used to derive a rotational motion the total number of revolutions ofwhich is proportional to the summation of the Ats required in carryingout the objectives of my invention in the manner described;

FIG. 3 shows schematically the principle of the bombsight and one methodof injecting the time correction into the sight mechanism according tomy invention;

FIG. 4 shows a schematic electrical Wiring diagram of a preferredembodiment of my invention which may conveniently be applied to aconventional Norden bombsight;

FIG. 5 shows a schematic diagram of the mechanical system of FIG. 4illustrating the manner in which the purpose of my invention may beaccomplished on the Norden bombsight; and

FIG. 6 shows a speed vs. voltage characteristic curve of one of themotors shown in FIG. 4.

Referring to FIG. 2, numeral 1 indicates the frame of an integratingdevice of a well-known type in which a smooth-faced disc 2 iscontinuously rotated about an axis normal to the plane of the figure ata constant predetermined speed by any suitable type of drive such as aconstant speed governor-regulated D.-b. motor operating from theairplane power source. A suitable planimeter wheel 3 is carried by acarriage 9 sliding on guide rods 9a. The position of the carriage 9 maybe adjusted through lead screw 8 by a manually or otherwise driven dial7, such that the radial position of the planimeter wheel contact on thedriving disc 2 may be varied from zero to any desired radius. Thepurpose of this adjustment will be brought out later.

The rotation of the planimeter wheel is transmitted through a suitablereduction gearing 4, 5, to an output shaft 6. Shaft 6 has a keywaythroughout its length and the shaft gear has a key which engages thekeyway so as to transmit rotation to the shaft 6 at any position of thecarriage 9. Interposed in shaft 6 is a magnetic clutch 59, so that theoutput shaft 60 is stationary except when the magnetic clutch 59 isenergized, in which case, it rotates with shaft 6.

In operation, the driving disc 2 is rotating continuously at apredetermined constant speed, and this together with the radial positionof the planimeter wheel adjusted by dial 7, comprises an adjustableconstant-speed drive to the shaft 6. Thus, if the magnetic clutch 59 isenergized each time, and for the duration of, the up-elevator control U,connected mechanically or electrically to the bombardiers control stick,the total number of revolutions of the shaft 60 will be an integratedmeasure of the total elevator application applied to the bomb. Outputshaft 60 is connected through a suitable bevel gear 10 to shaft 11 intoa differential gear box 12, thence through differential gear box 15 tothe final output shaft 18.

Into differential gear 12 through shaft 14 and magnetic clutch 13 is fedthe output of a second integrator identical with the up-elevatorintegrator 1, except that, by a suitable selection of gear ratios, thespeed of shaft 61 in relation to that of shaft 6 is determined by theratio of the up-elevator coeflicient a to the down-elevator coeflicientc referred to in the earlier discussion. Magnetic clutch 13 serves toengage shaft 14 with 61 whenever the down-elevator control D is applied.Differential gear 12 thus delivers to its output shaft 63 the sum ofrotation of shafts 11 and 14. Similarly, the output 62 of a thirdintegrator of identical type, whose clutch is actuated by application ofeither R or L rudder controls through magnetic clutch 16 to shaft 17,feeds through differential gear 15. The speed of this third or rudderintegrator is designed, by proper gear ratios, to be in the ratio ofcoefficients a and b referred to earlier.

Finally it will be evident that, with the proper selection of discspeeds and/or gear ratios for the three integrators, the total number ofrevolutions of shaft 18 will be proportional to the summation of theincremental Ats due to all rudder and elevator control applications, andis therefore proportional to the displacement of the mirror from thatnormally required in the bombsight, that is, to the correction requiredto delay coincidence of the two lines of sight.

FIG. 3 shows schematically the essential features necessary in theapplication of the corrector mechanism to the bombsight. Here 19 is thesighting telescope which in the Norden type sight is gyro-stabilized sothat the line of sight 22 through the partial mirror 20 is heldsubstantially in the vertical or alternatively backward along the trailangle of the falling bomb 23. Partial mirror 20 is pivotally mounted onan axis 65 normal to the plane of the figure so that the angle betweenthe line of sight 24 to the target and the vertical 22 may be varied.Partial mirror 20 is connected by drive 26 through a differential gearbox 27 to the shaft 28 which is driven by the usual bombsight mechanismand which provides a motion to the mirror 20 suitable for continuoustracking of the target in the conventional manner.

In the final assembly of the sight correcting device the output of thecorrector shaft 18, FIG. 2, is put into 9 the differential 27, FIG. 3,through shaft 66, FIG. 3. The mechanical connection from the correctoroutput 18, FIG. 2 to 18 FIG. 3 may be by flexible shafting or otherconvenient means. A manually operated clutch 30 or alternatively amagnetically operated clutch is interposed between shafts 18 and 66 andserves to disengage the entire corrector mechanism of FIG. 2 beyondshaft 18 and locks shaft 66 so as to permit normal adjustments of thebombsight prior to release of the bomb. After release, clutch 30 isengaged (or a magnetic type clutch may be connected to automaticallyengage whenever steering controls are applied) and thereafter anyoperation of the bomb steering controls will superpose on the normalmotion of the tracking mirror 20 a lag displacement calculated to delaycoincidence by the appropriate incremental time necessary to achievecorrection of the bombardiers sighting angles in accordance with thedelayed fall of the bomb.

Evidently the relative speeds of the component parts of the correctormechanism compared with the normal bombsight mechanism must be properlyselected in order that the proper amount of correction be applied.However, to one skilled in the art this is a detail of design notpertinent to the principles of my invention. It should be sufiicient tosay that the corrective angular motions of the mirror that are requiredto correct the timing are small and over the duration of a fullycontrolled drop, may never exceed about 2 total angular motion. Thus, a1 mirror correction would correspond to an ap parent shift of the targetof 35 mils or 535 ft. ground displacement as viewed from 15,000 ft.

In FIG. 2, the dial 7 serves to vary the position of the planimeterwheel 3 on the radius of the main driving disc 2. Similar adjustmentsexist on the other component correctors and they serve to vary theoutput speed of the mechanism in accordance with the setting of thedial. Now it may be shown that the total correction applied to thebombsight should be proportional to the T.D.A. (tangent of the droppingangle) of the sight plus the trail angle set into the sight. Thus, whilethe coeflicients a, b and c which represent the time delays in the fallof the bomb have a constant value for a given type of bomb, thecorrection introduced into the sight for a T.D.A. of, say, 0.5 should be/2 that required if the indicated T.D.A. of the sight were 1.0. Thetangent of the dropping angle (T.D.A.) is related to the ground speed ofthe bombing plane and therefore to the ground speed of the bomb. Hencethe dial 7 is calibrated in T.D.A. units such that at a T .D.A.=0, theplanimeter wheel is at zero radius on the disc 2' (except for the trailangle correction) and at any other T.D.A. it will be at aproportionately greater radius so that the speed of the output shaft 6will be proportional to the T.D.A. setting as required. The T.D.A. is aquantity whose value may be obtained from the bombsight in conventionalmanner. The correction for the fixed trail angle may be introduced byoffsetting the Zero of the scale on dial 7 in such manner that with theT.D.A. dial set at zero, the planimeter wheel 3 is not exactly at zeroradius on disc 2 but is at a point corresponding to the trail angle.Thus any setting of the T.D.A. dial will provide a speed of the outputshaft 6 proportional to the T.D.A. plus trail angle. The trail angle hasa fixed value for any given type of dirigible bomb and may be set withthe permanent adjustments of the sight when such type bombs are beingused.

In practice, the T.D.A. dials of all three units are coupled together sothat only one dial need be adjusted to the proper value. This value andthe setting of the corrector T.D.A. dial is made by the bombardierimmediately after release of the bomb when the T.D.A. of the drop isindicated by a suitable index on the Norden sight. Moreover, since thisindicated value is repeated exactly by the angular position of one ofthe adjusting knobs on the sight (ordinarily manually set by thebombardier in his synchronizing adjustment) the T.D.A. dials of thecorrector may be connected directly to his synchronizing adjuster of thebombsight by means of a suitable coupling shaft or other obvious means,Whereby the proper setting of the corrector is automatically changed tocorrespond with the T.D.A. of the sight. This method is preferred sinceit eliminates one manual operation in the bombsight adjustment.

While the above described corrector mechanism is illustrative of oneembodiment of the bombsight time corrector principle, it represents onlyone apparatus for accomplishing the desired result. Evidently manymechanical modifications may be made without departing from theprinciples of this invention. A preferred embodiment of my invention,shown in FIGS. 4 and 5, has advantages of convenience in being simply anattachment which may be added to the Norden bombsight mechanism Withoutmodification of any details of the sight itself. 'In this embodimentadjustable but relatively constant speed electric motors are used toperform the integration of the steering effects, one such electric motortaking the place of each of the units 1 of FIG. 2. This effectsconsiderable simplification as will be apparent.

FIGURE 4 shows a schematic electric wiring diagram of the simplifieddevice adapted for use on the Norden sight. Switches 35, 36, 37 areconnected to the bombardiers bomb control stick, either throughmechanical connections or by auxiliary relays, and are respectively"closed whenever the bombardier imparts to the bomb left-rudder,right-rudder or up-elevator steering control. The switches 35, 36, 37control the electric motors whose properly integrated revolutions give ameasure of the steering corrections applied to the bomb and hence alsoof the resulting timing correction required to be made on the bombsight.

A further simplification may be effected by omitting, as in FIG. 4, theprovision for correction of the sight mechanism timing in accordancewith down-elevator applications. This may be done because in most casesthe additional downward acceleration of the bomb due to down-elevatorapplication is approximately equal to the deceleration resulting fromthe added induced drag. Thus it is true that within the overallapproximations involved in the time correction method here used, theeffect of down-elevator may be ignored in practice. However. it will beevident that in case the down-elevator factor should be important incertain types or designs of dirigible bombs, an additional correctorunit may be superimposed on the system of FIGS. 4 and 5 in the samemanner as the rudder and elevator units described.

In FIG. 4, 31 and 32 represent two small permanent magnet type D.-C.motors Whose speed vs. voltage characteristics are linear orsubstantially so. This linear characteristic, shown as curve 49, FIG. 6,has an intercept 50 which represents the voltage which must be appliedto overcome friction in the motor. Thus, if a residual bias voltageequal to this intercept is permanently applied to this type motor, thespeed vs. voltage characteristics may be made to pass through the Zeropoint as curve 51. Hence with a permanent bias of this kind applied, thespeed of the motor will be linearly proportional to any additionalvoltage applied at the motor terminals, that is its speed vs. voltagecharacteristic will then be similar to curve 51. The necessity for thischaracteristic Will become evident later.

In FIG. 4 motors 31 and 32 are connected to relays 33 and 34respectively and in such fashion that on closing either switch 35 or 36motor 32 will operate and similarly, the closing of switch 37 causesmotor 31 to operate. Switches 35 and 36 close in response to thebombardiers left and right rudder controls while switch 37 closes onapplication of up-elevator, these switches being connected to thebombardiers bomb control stick either mechanically or by relays.

The relay armature springs 70b, 70d of relay 33 and 71b, 71d of relay 34are shown in FIG. 4 in the deenergized position against the upper set ofcontacts 70a, 700 of relay 33 and 71a, 710 of relay 34 respectively. Itis apparent that on closing switch 35 or 36, current from the battery 69energizes relay coil 34, and springs 71b, 71a are drawn down to thelower set of contacts. Motor 32 is thereupon supplied with power fromthe positive side of the battery 69 as follows: wire 72, resistor 40,wire 73, wire 74, contact 71c, spring 71d, wire 75, motor 32, wire 76,wire 78 and return to battery 69. Similarly on closing switch 37 currentfrom battery 69 energizes relay coil 33 and spring 70b, 70d are drawndown to the lower set of contacts. Motor 31 is thereupon supplied withpower from battery 69 as follows: wire 72, resistor 40, wire 73, wire74, contact 70e, spring 70d, wire 77, motor 31, wire 76, wire 78, andreturn to battery 69.

It will be noted in FIG. 4 that when the motor actuating relays 33, 34are not energized, the armatures of the respective motors 31, 32 areshort circuited. Since these motors have permanent magnet fields, thisshort-circuit elicits electrodynamic braking and thus prevents anycoasting of the motors. This feature is desirable since the total numberof revolutions of the motor is in this embodiment used as an integrationmeasurement. Upon de-energizing relay 34, spring 71d returns to contact710 and a short circuit is thus immediately placed on the motor armature32 via wire 75, spring 71d, contact 710, wire 78 and wire 76. Similarlyde-energizing relay 33 allows spring 70d to return to contact 700 andplaces a short circuit on motor armature 31 via wire 77, spring 70d,contact 700, wire 78 and wire 76. It is apparent that the operations ofmotors 31 and 32 may be carried out independently or simultaneously asis dictated by the bombardiers steering effects.

In FIG. 4 resistances 40 and 41 are connected in series as a voltagedivider across a D.C. power supply 69, the adjustable tap on resistor 40permitting any desired voltage to be applied to the motors. In order toavoid any fluctuations of motor voltage when one or the other motor isturned on or off, the resistors 38 and 39 are placed in the circuit asdummy loads which replace the motor loads when the relays are notenergized. They are adjusted to match the normal motor loads and thusprevent any serious change in the measured voltage drop across thevoltage divider 40, 41 when the motor are actuated. Thus from wire 74there exists either a load through resistor 39, contact 70a, spring 70bto wire 78 or else through the motor 31 armature as previously traced,and similarly for resistors 38 or motor 32.

A voltmeter instrument 43 calibrated in T.D.A. (tangent of the droppingangle) from -1.1 or 1.2 in effect measures the voltage applied to themotors minus the voltage drop across the small adjustable resistor 41.Thus, the motors are always subjected to voltage greater than that readby the T.D.A. meter by an amount equal to the voltage drop across 41.This is the bias voltage previously referred to whereby the speed of themotors may be made proportional to the T.D.A. voltage over the completerange of from 0 to full-scale values.

It will thus be evident from FIG. 4 that on closing switch 37 actuatedwhen the bombardier applies up-control in steering a bomb, motor 31 willrotate at a speed directly proportional to the T.D.A. meter reading 43.Moreover, if the tap on divider 40 is adjusted so that the T.D.A. meterreading 43 is identical with the T.D.A. of the bombsight at release, thetotal number of revolutions made by this motor will be proportional tothe incremental time of fall of the bomb due to up-elevator applicationsmultiplied by the T.D.A. of the drop as required of the correctormechanism. Similarly, applications of right or left rudder will actuatemotor 32 with a similar integration of the incremental time lag of thebomb caused by rudder applications.

This information, in the form of total number of revolutions of therespective motor shafts, must be applied to the bombsight additively toalfect the desired delay in the sight coincidence. In this embodiment itwas found most expedient to apply the correction directly to the rateknob of the Norden sight. (See US. Army Air Forces publication entitledBombsights-M-Series Types M-9A and M9BModification and Operation,Technical Order No. ll3073 of June 29, 1945.) To those familiar with theart, this expedient means will be readily understood. It is sufficienthere to explain that the rate knob or synchronizing knob of the Nordensight affects an adjustment of the angular speed of the target-mirror20, FIG. 3. The effect of applying the correction to the rate knob ascompared to a direct displacement of the mirror as in the method of FIG.3, is that the Norden sight mirror mechanism already comprises anintegrating device. Thus, a correction applied to the rate knob changesthe mirror rate throughout the remaining time of flight of the bomb.Accordingly, the coefiicients a, b, and c for this type corrector mustbe derived from the empirical data with this integrating mechanism inmind, and they will have not only different numerical values butmathematical functions of different character than in the case of adirect displacement corrector as in FIG. 3.

However, in either the displacement method or the rate knob method ofapplication of correction, I have found that suitable correctioncoefiicients can be derived.

The mechanical connection between the corrector motors 31 and 32 of FIG.4 is shown schematically in FIG. 5. Here the motors are shown connectedthrough individual reduction gears 44 and 45 to a differential gear 46such that the rotation of the output shaft 48 represents the summationof the speeds of the individual motors. Output shaft 48 connects to therate knob of the N01- den sight by a suitable gear with a manuallyoperated friction clutch 47 interposed to permit normal manualadjustment of the rate knob during the bombardiers target-synchronizingoperation. At release of the bomb the corrector mechanism is clutched inand automatic time correction proceeds.

As an example of the numerical factors involved, in the specificembodiment of the device illustrated in FIG. 5 designed for a specificdirigible bomb (VB-3), the speeds at which the rate knob should beturned are:

For up-elevator- Rate knob speed=514.3(T.D.A.-l-trail)a=degrees/sec.

For 1'udder-- Rate knob speed=514.3 (T.D.A.-I-trail)b=degrees/sec. wherea and b are coefficients determined from actual drop data as alreadymentioned, and the trail is the rearward tilt of the line of sight tothe bomb (a normal value of which is 45 mils).

Examples of typical values of the coefiicients a and b are: a=0.0088 andb=0.0035

At a T.D.A. setting of 0.70, the rate knob speeds are therefore:

For up-elevator corr.=514.3 (0.70+0.04S)0.0088=3.38

sec. For rudder corr.=514.3(0.70+0.045)0.0035=1.34/sec.

The permanent-magnet fields of the two motors 31 and 32 may be adjustedso that they have equal speeds at any given voltage. Then in FIG. 5, thegear train of motor 31 through 44 and 46 may be designed so as tocompare with the gear train of motor 32 through 45 and 46 in the ratioof the coeflicients a and b. As an example, to fit the values of a and babove given, one may use a reduction of 10,7116/1 for motor 31 and areduction of 26,733/1 for motor 32. Moreover, the actual speed of themotors at the voltage corresponding to a T.D.A. meter reading of 0.70may be adjusted to:

3.38 x 10,716/360: 100.6 rev./sec.=6036 r.p.m. approx.

Under these conditions, the sight corrector will then apply to the rateknob an appropriate rotation to delay the motion of the target mirrorinto the vertical by an incremental time equal to the total time laginduced in the fall of the bomb due to the applications of rudder andupelevator controls during steering.

It will be noted from the above equations that the desired rate knobspeed involves a factor: (T.D.A.+trail) the trail being a fixed valueequal to the trail angle previously mentioned. (The trail angle and thetangent of the trail angle are substantially equal since this angle isalways small.) Since this is a constant value in any given sight fordirigible type bombs this factor is introduced in the T.D.A. meter 43 ofthe corrector by merely calibrating the meter so that its mark is to theright of the no-current point of the meter. The meter may then haveT.D.A. calibrations to the right of the O and trail readings to the leftof the O. The trail value may then be adjusted if necessary by adjustingthe no-current zero position of the meter in the customary way, in thisway setting the no-current zero of the meter needle to the appropriatetrail value. Consequently, when the resistor 40 is adjusted to give aT.D.A. meter indication on the meter dial, the actual voltage used willthen be the T.D.A. voltage plus the trail voltage as required. Thisvoltage will exist across the left-hand part of resistor 40 of FIG. 4,and is the voltage abscissae of curve 51 of FIG. 6. The actual voltageapplied to the motors (between wire 74 and 78) will be this voltage plusthe voltage drop across resistor 41, FIG. 4, this total beingrepresented by the abscissae of curve 49, FIG. 6.

An additional detail concerns the purpose of the adjustable resistor 42in series with the T.D.A. meter 43 of FIG. 4. This is an expedientmethod of introducing minor corrections as, for example, the effect ofaltitude on the incremental time lags. It has been found that thenumerical value of the corrector coeflicients changes slightly withaltitude. This effect may be compensated adequately by proper adjustmentof resistor 42, whereby the effect of a change in the numerical value ofthe corrector coefiicients may be made conveniently. The dial on thisresistor may be calibrated to read altitude.

I do not limit the scope of my invention to the particular apparatusembodied in the above disclosures. For example, in FIG. 2 it will beevident that the dial 7 may be used as an adjustment to match the outputspeed to any particular value of correction factor a, with similaradjustments in the several corrector units to match coefficients 1: and0. Alternatively, in the embodiment of FIG. 2, the required speed vs.T.D.A. adjustment may be accomplished by simultaneously varying thespeed of the discs 2 in accordance with the T.D.A. value. These andother modifications of the mechanical or electrical details may be madewithout departing from the spirit of my method of time correction ofdirigible-bomb sights.

What I claim as my invention is:

1. In a bombsight having a time-controlled mechanism for closing thelines of sight to the bomb and to the target and adapted to be used forrange control of dirigible bombs, apparatus for correcting theprediction of the closing time of the line of sight to the bomb with theline of sight to the target such that said closing time will coincidewith the impact time of the bomb which comprises means for generating amotion which is proportional to the change in dropping time of the bombinduced by steering thereof, means actuated by said generating means fortransmitting said motion whenever steering influences are imparted tothe dirigible bomb and means combining said transmitted motion with thenormal motion of the bombsight line-of-sight-closure mechanism wherebythere is introduced into the closure time of the lines of sight a timechange substantially equal to the change in the dropping time of thebomb induced by steering thereof.

2. In a bombsight having a time-controlled mechanism for closing thelines of sight to the bomb and to the target and adapted to be used forrange control of dirigible bombs, apparatus for correcting theprediction of the closing time of the line of sight to the bomb with theline of sight to the target such that said closing time will coincidewith the impact time of the bomb which comprises means for generating amotion which is proportional to the change in dropping time of the bombinduced by steering thereof, means for adjusting said generating meansso that said motion is proportional to the sum of the tangent of thedropping angle at release of the bomb and the trail angle setting of thebombsight, means actuated by said generating means for transmitting saidmotion whenever steering influences are imparted to the dirigible bomband means combining said transmitted motion with the normal motion ofthe bombsight line-of-sight-closure mechanism whereby there isintroduced into the closure time of the lines of sight a time changesubstantially equal to the change in the dropping time of the bombinduced by steering thereof.

3. In a bombsight having a time-controlled mechanism for closing thelines of sight to the bomb and to the target and adapted to be used forrange control of dirigible bombs, apparatus for correcting theprediction of the closing time of the line of sight to the bomb with theline of sight to the target such that said closing time will coincidewith the impact time of the bomb which comprises means for generating amotion which is proportional to the change in dropping time of the bombinduced by upward steering thereof, means for generating a motion whichis proportional to the change in dropping time of the bomb induced bydownward steering thereof, means for generating a motion which isproportional to the change in dropping time of the bomb induced by rightand left steering thereof, means actuated by said generating means fortransmitting said motions whenever said steering influences are impartedto the dirigible bomb and means combining said transmitted motions withthe normal motion of the bombsight line-of-sight-closure mechanismwhereby there is introduced into the closure time of the lines of sighta time change substantially equal to the change in the dropping time ofthe bomb induced by steering thereof.

4. In a bombsight having a time-controlled mechanism for closing thelines of sight to the bomb and to the target and adapted to be used forrange control of dirigible bombs, apparatus for correcting theprediction of the closing time of the line of sight to the bomb with theline of sight to the target such that said closing time will coincidewith the impact time of the bomb which comprises means for generating amotion which is proportional to the change in dropping time of the bombinduced by upward steering thereof, means for generating a motion whichis proportional to the change in dropping time of the bomb induced bydownward steering thereof, means for generating a motion which isproportional to the change in dropping time of the bomb induced by rightand left steering thereof, means connected to said generating means foradjusting said motions whereby they may be made proportional to the sumof the tangent of the dropping angle at release of the bomb and thetrail angle setting of the bombsight, means actuated by said generatingmeans for transmitting said motions whenever said steering influencesare imparted to the dirigible bomb and means combining said transmittedmotions with the normal motion of the bombsight line-of-sightclosuremechanism whereby there is introduced into the closure time of the linesof sight a time change substantially equal to the change in the droppingtime of the bomb induced by steering thereof.

5. In a bombsight having a time-controlled mechanism for closing thelines of sight to the bomb and to the target and adapted to be used forrange control of dirigible bombs, apparatus for correcting theprediction of the closing time of the line of sight to the bomb with theline of sight to the target such that said closing time will coincidewith the impact time of the bomb which comprises means for generating anangular motion functionally related to the duration and direction ofsteering influences imparted to the bomb and proportional to the sum ofthe tangent of the dropping angle at release of the bomb and the trailangle setting of the bombsight and means actuated by said generatingmeans for introducing said angular motion into the normal motion of thebombsight line-of-sight-closure mechanism whereby there is introducedinto the closure time of the lines of sight a time change substantiallyequal to the change in dropping time of the bomb induced by steeringthereof.

6. In a bombsight having a time-controlled mechanism for closing thelines of sight to the bomb and to the target, said mechanism having anadjustment for its rate of closure, and adapted to be used for rangecontrol of dirigible bombs, apparatus for correcting the prediction ofthe closing time of the line of Sight to the bomb with the line of sightto the target such that said closing time will coincide with the impacttime of the bomb which comprises means for generating a motion which isproportional to the change in dropping time of the bomb induced byupward steering thereof, means for generating a motion which isproportional to the change in dropping time of the bomb induced by rightand left steering thereof, means actuated by said generating means fortransmitting said motions whenever said steering influences are impartedto the dirigible bomb to the rate-ofclosure-controlling adjustment ofthe bombsight.

7. In a bombsight having a time-controlled mechanism for closing thelines of sight to the bomb and to the target, said mechanism having anadjustment for its rate of closure, and adapted to be used for rangecontrol of dirigible bombs, apparatus for correcting the prediction ofthe closing time of the line of sight to the bomb with the line of sightto the target such that said closing time will coincide with the impacttime of the bomb which comprises means for generating a motion which isproportional to the change in dropping time of the bomb induced byupward steering thereof, means for generating a motion which isproportional to the change in dropping time of the bomb induced by rightand left steering thereof, independent speed-adjusting means connectedto each of said motion-generating means for adjusting said motionswhereby they may be made proportional to the sum of the tangent of thedropping angle at release of the bomb and the trail angle setting of thebombsight, means actuated by said generating means for transmitting saidmotions whenever said steering influences are imparted to the dirigiblebomb to the rate-of-closure-controlling adjustment of the bombsight.

8. In a bombsight having a time-controlled mechanism for closing thelines of sight to the bomb and to the target, said mechanism having anadjustment for its rate of closure, and adapted to be used for rangecontrol of dirigible bombs, apparatus for correcting the prediction ofthe closing time of the line of sight to the bomb with the line of sightto the target such that said closing time will coincide with the impacttime of the bomb which comprises a source of electric power, a constantspeed electric motor, an electric switch means connecting said motor tosaid source of power whenever a steering influence is imparted to thedirigible bomb, a gear train transmitting the total motion of said motorto the rate-ofclosure-controlling adjustment of the bombsight in a ratiorelated to the change in dropping time of the bomb induced by steeringthereof.

9. In a bombsight having a time-controlled mechanism for closing thelines of sight to the bomb and to the target, said mechanism having anadjustment for its rate of closure, and adapted to be used for rangecontrol of dirigible bombs, apparatus for correctingthe prediction ofthe closing time of the line of sight to the bomb with the line of sightto the target such that said closing time will coincide with the impacttime of the bomb which comprises a source of electric power, a constantspeed electric motor, an electric switch means connecting said motor tosaid source of power whenever a steering influence is imparted to thedirigible bomb, an adjustable gear train including differential gearmeans for transmitting the total motion of said motor to therate-of-closurecontrolling adjustment of the bombsight in a ratiorelated to the change in dropping time of the bomb induced by steeringthereof and with said ratio adjusted to be proportional to the sum ofthe tangent of the dropping angle at release of the bomb and the trailangle setting of the bombsight.

10. In a bombsight used for range control of dirigible bombs, apparatusfor correcting the prediction of the closing time of a line of sight tothe bomb with a line of sight to the target such that said closing timewill coincide with the impact time of the bomb which comprises means forgenerating a motion proportional to the duration of a component ofsteering influence imparted to the bomb, means for adjusting saidmotion-generating means whereby said motion may be made proportional tothe sum of the tangent of the dropping angle at release of the bomb andthe trail angle setting of the bombsight, means actuated by saidmotion-generating means for adjusting the angle between the bombsightlines of sight by an amount proportional to said motion and in a ratiorelated to the change in dropping time of the bomb induced by steeringthereof.

11. In a bombsight used for range control of dirigible bombs, apparatusfor correcting the prediction of the closing time of a line of sight tothe bomb with a line of sight to the target such that said closing timewill coincide with the impact time of the bomb which comprises means forgenerating a motion proportional to the duration of a component ofsteering influence imparted to the bomb, means controlled by saidmotion-generating means for reducing the rate of decrease of the anglebetween the bombsight lines. of sight by an amount proportional to saidmotion and in a ratio related to the change in dropping time of the bombinduced by steering thereof.

12. In a bombsight used for range control of dirigible bombs, apparatusfor correcting the prediction of the closing time of a line of sight tothe bomb with a line of sight to the target such that said closing timewill coincide with the impact time of the bomb which comprises means forgenerating a motion proportional to the duration of a component ofsteering influence imparted to the bomb, means for adjusting saidmotion-generating means whereby said motion may be made proportional tothe sum of the tangent of the dropping angle at release of the bomb andthe trail angle setting of the bombsight, and means controlled by saidmotion-generating means for reducing the rate of decrease of the anglebetween the bombsight lines of sight by an amount proportional to saidmotion and in a ratio related to the change in dropping time of the bombinduced by steering thereof.

References Cited in the file of this patent UNITED STATES PATENTS1,114,705 Boykow Oct. 20, 1914 2,118,041 Estoppey May 24, 1938 2,162,698Chafee et al June 20, 1939 2,404,746 Rylsky et a1. g July 23, 19462,428,678 Norden et al Oct. 7, 1947 2,438,532 Barth Mar. 30, 19482,459,919 Clark Jan. 25, 1949

